MICROCHEMISTRY OF IMPACT MELT GLASSES OF LONAR CRATER, INDIA

The Lonar Crater of India, the only well-preserved terrestrial simple crater in Deccan flood basalts. Though the crater was primarily identified by its classical morphological features, but yet lacking in explicit petrographic and geochemical signature of the impact. Neither any shocked minerals have been identified in the ejecta nor any obvious geochemical of impactor. Elemental and isotopic analysis of the different optical phases of the glass samples collected from the rim of the Lonar crater were analyzed by using Agilent 8900 ICP-MS Triple Quad, using Helium as a collision gas and ESI NWR 193 nm ArF eximer laser with 30um spot size, in order to assess further the type of extraterrestrial components and the fractionation of impactor and the target materials. Present analysis of glass spherules collected from the ejecta rim was variability in the concentration of ⁵³Cr (2.55~11.34 ppm), ⁵⁵Mn (32.78 ~ 125.86 ppm), ⁵⁹Co (3.1~5.93 ppm), ⁶⁰Ni (2.24~ 7.14 ppm), ⁶³Cu (4.48 ~ 16.14 ppm), ⁶⁶Zn (1.53 ~ 8.2 ppm), ⁵⁶Fe (1024 ~ 6315 ppm), ⁸⁸Sr (30.7~44.97 ppm) and ¹³⁷Ba (176~228 ppm). Results of the present analysis is not consistent with the earlier analysis of the glass spherules.

Chromium isotopic ratio of ⁵³Cr/⁵²Cr in the glass sample varies between 0.61 to 0.9, due to the variable concentration of 53Cr. Whereas the host and altered materials of the ejecta rim shows significantly lower ratio of ⁵³Cr/⁵²Cr, i.e. 0.023 to 0.05. Higher concentration of ⁵³Cr and Mn/Cr ratio (11.6~19.1) of the studied glass spherules samples suggest ordinary L chondrite as the impactor of Lonar crater.